I think the argument here isn't to reread a trigonometry book until you get it, regardless of your knowledge of the prereqs. The message I took is to find the book written by a/the master in the field of trigonometry, living or dead, in order to learn trig. If you don't yet understand geometry which is needed to understand trig, then find a book by the most renowned scholar in geometry.

It's sort of like that telephone game we play in elementary school, where the message gets passed around the room and ends up nothing like it started. Learn from the source of these insights, not from someone else who learned it and is giving you their interpretation.